Typical conventional optical discs include CDs, DVDs, and the like. Among others, a DVD-RAM, i.e., a rewritable optical disc, includes a bar-code area (BCA) having a form of a bar code for recording copyright protection information or a serial number on an innermost periphery, a control track (LEAD-IN area) adjacent to the BCA which is pre-cut with a concave-convex emboss, a gap area adjacent to the LEAD-IN area which is formed by a mirror portion formed all the way around, and data tracks adjacent to the gap area which have a continuous trench-like structure called lands and grooves. The data tracks are separated along a peripheral direction into regions of every predetermined block, which are called sectors, with preformatted address portions having zigzag mark (pit) forms.
For compatible recording capacity and performance, the rate of an optical disc is changed in a predetermined length of the diameter. Herein, in order to achieve a substantially constant linear velocity of an optical disc during driving, the optical disc is divided into 35 regions (24 regions in Ver. 1.0) which are called zones along the radial direction. On the innermost periphery of the data track of the optical disc, a TEST zone for learning a recording power or the like of the laser in accordance with the optical disc is provided. Adjacent to the data tracks of innermost periphery and the outermost periphery, DMAs (Disk Management Areas) for managing defects are provided.
For actually recording information on a DVD-RAM disc, an optical beam is moved to the emboss region to read control data and to collect required data related to the disc or recording conditions and so on. The recording power of the laser or the like is learnt in the TEST zone. Then, information of the inner and the outer DMAs are read and the information is updated for preparation. Basically, when a predetermined request for writing data is issued, recording is performed sequentially from an inner data track. Every time an optical beam crosses a border of the zones, the rate is reduced to maintain the linear velocity constant while the recording is performed.
Regarding a read-only DVD-ROM, a double-layer disc, in which an information surface having a pit shape is provided on a substrate having a thickness of 0.6 mm is standarilized and two such substrates are attached to each other in the same direction, allowing information to be read from one side without reversing the disc. The layout of the DVD-ROM disc is basically the same as that of the DVD-RAM. Similar to the DVD-RAM described above, a DVD-ROM has a BCA having a bar code shape in which copyright protection information and a serial number are recorded on the innermost periphery of the disc, and adjacent to the BCA, a control track (LEAD-IN) which has a pre-cut embossed shape. A data portion which has the same embossed shape is physically coupled to the control track.
A recording layer L0 is closer to a source of an optical beam (a light source) than a recording layer L1. An intermediate layer between the recording layer L0 and the recording layer L1 generally has a thickness of 40-70 μm. Movement between the layers is realized by focus jumping, i.e., switching off tracking control temporarily, releasing focus control, and applying a pulse having a rectangular wave shape to a focus actuator. In general, a direction for recording information on a disc is a direction from the inner periphery to the outer periphery of the disc for both the L0 and L1 (parallel paths). However, it may be a direction from the inner periphery to the outer periphery for the L0 and vice versa for the L1 (opposite paths). The opposite paths allow the shortest focus jumping from L0 to L1 at the outer periphery of the disc even when a reproduction time of video data becomes long. Thus, seamless reproduction is possible.
However, regarding the above-mentioned recordable DVD-RAM disc, a double-layer disc or a multi-layer disc having two or more layers with information surfaces laminated does not exist. Conventional DVD-ROM double-layer discs include a parallel path type disc in which data is recorded in the same direction, from the inner periphery to the outer periphery, for both the L0 and L1, and an opposite path type disc in which data is recorded from the inner periphery to the outer periphery for the L0, and vice versa for the L1. If a multi-layer recordable disc is assumed based on this conventional technique, regarding a DVD-RAM disc, similar to a DVD-ROM double-layer disc, there may be a parallel path type structure in which recording surfaces are laminated in a simple manner with spiral directions thereof aligned, and an opposite path type structure in which recording surfaces are laminated with their spiral directions reversed.
In the case where a long-duration content is recorded on a parallel path type disc, when the recording is performed and reaches the outermost periphery of a recording layer closer to a light source (L0), an optical beam must go back to the innermost periphery of a recording layer further from the light source (L1). In addition to focus jump for moving between the L0 and L1, a seek of a full length stroke occurs. During the movement between the layers, data cannot be recorded and must be stored in a buffer memory. Thus, a large quantity of memory is required. However, when a large number of small-size files are recorded or reproduced at random, since they can be recorded closely to each other from the inner periphery. Thus, a latent time for motor rotation response becomes shorter every time the optical beam crosses borders between the zones. The reproduction performance is less effected by the motor response. In the case of the opposite path type disc, recording is performed until it reaches the outermost periphery of the L0 layer, and then it is resumed from the outermost periphery of the L1 layer. Thus, an ability to allow a random access is lower than that of the parallel path type disc in which recording is performed in the direction from the inner periphery to the outer periphery for both the L0 and L1.
The present invention is provided for solving the above-described problem. An objective of the present invention is to provide an optical disc which enables an efficient recording/reproduction regardless of a capacity of a file and allows both seamless data and a random access to data, and an information recording/reproducing method and information recording/reproduction apparatus using the same.
In order to improve a density (capacity) and further secure SN of a reproduction signal, generally, track pitches are made closer to each other and depths of grooves are made shallower. This results in reduction in an amplification of a push-pull tracking error signal. Further, due to an influence of light reflected off adjacent tracks having different reflectances while data is recorded, an offset is generated in a tracking error signal.
A conventional optical disc has a one-spiral structure. When data is continuously recorded in this track, recording proceeds sequentially from, for example, track 1 of the inner periphery, to adjacent tracks along the spiral. When the continuous recording is performed as such, relative to a current position of a beam spot performing recording, the inner adjacent track has been recorded and the outer adjacent track remains unrecorded. The inner and the outer adjacent tracks have different reflections. Conventionally, in a scheme where a track deviation is detected using intensities of first-order diffracted light at track groove portions, such as, a push-pull tracking, such an influence of a difference in reflectances between adjacent tracks have been small. As the density becomes higher and track pitches become smaller, a relative diameter of a spot of an optical beam with respect to a track on the disc becomes large. Thus, due to an influence caused by a difference in reflectances of adjacent tracks, an offset is generated in a tracking signal. The tracking tends to go off easily. Accordingly, a skip of sounds and a block noise may undesirably occur when the beginning of a music piece or video is being searched or when the reproduction thereof comes to an end.
The present invention is provided for solving the above-described second problem. An objective of the present invention is to provide an apparatus having a high reliability by recording information on every other track to reduce an influence caused by a difference in reflectances due to recorded/unrecorded states of adjacent tracks and implement a stable track control.
Another objective of the present invention is to implement a partial ROM disc more easily by locating a ROM region on the layer furthest from the light source to provide a high performance apparatus which is capable of record and reproduce with fast switching between a ROM region and a RAM region and implementing a fast-speed recording of additional data or recording a program different to the one being viewed.